Metallic core wiring substrate

ABSTRACT

A metallic core printed circuit board having a number of lead terminals such as IC or LSI lead terminals provided on at least one edge of an electrically conductive substrate which forms a core by etching or other process. The respective terminals are electrically insulated from and secured to the core by an insulating binder, and then either conductor circuit patterns are directly formed on or a printed board wherein a printed circuit has been completed is bonded to the layer of the insulating binder. The metallic core printed circuit board makes it possible to increase a packaging density of required components, to allow easy connection to other circuit boards such as a mother board and the like, and to reduce a volume of the circuit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a metallic core wiring substrate, andparticularly to a metallic core wiring substrate which is suitable formanufacturing printed wiring used for packaging required components at ahigh density or for a hybrid integrated circuit (HIC).

2. Description of the Prior Art

A conventional metallic core wiring substrate which has been widely suedheretofore is manufactured by applying an insulating layer to thesurface of a metallic plate to form a core, and additional steps areperformed to define the required electrically conductive patterns,through holes or the like on the insulating layer. Accordingly, there isa disadvantage in that the manufacturing process is complicated with theresult that the products become expensive. In order to eliminate theabove described disadvantage, there has been proposed a method wherein aprinted board is directly bonded to the surface of a core metal andcomponents are then packaged on the printed board. However, with aconstruction according to the above method wherein circuit patterns areformed on the back of the surface of the printed board joined with thecore metal) of the printed board, and the circuit patterns are connectedwith components to be packaged on the surface of the printed board viathrough holes in order to increase the density of the components it isdifficult to maintain the insulation between the components and thecircuit patterns on the back of the printed board. Hence, the abovedescribed construction is hardly accepted, and furthermore, it involvesa disadvantage in that separate lead terminals must be further attachedto the printed boards if the provision of the lead terminals isrequired. Furthermore, since a pad is used at the connection between thelead terminals and the wiring patterns, the space for packaging thecomponents is narrowed by a width of the pad in the above describedconstruction, so that it cannot satisfy the requirement forminiaturization of the electronic circuit.

It has been heretofore common to employ a ceramic sheet or a plasticlaminate as the substrate for manufacturing a hybrid IC. However, such aceramic sheet itself is expensive, and in addition, a silver-palladiumpaste is required for forming electrically conductive patterns on thesheet, so that the resulting product becomes more expensive. Inaddition, when it is intended to utilize both surfaces of the ceramicsubstrate in order to elevate a wiring density, through holes arenecessary and the processing therefor is considerably troublesome.

On the other hand, the latter substrate, i.e. a plastic laminate, doesnot involve the problems as mentioned above, but a step for connectinglead terminals with the laminate is required in order to secure them inthis case also so that considerable time is necessary therefor.Furthermore, in the case where a metallic core printed circuit isvertically connected to a mother board through these lead terminals, theprinted circuit provided upright becomes higher by a heightcorresponding to a stationary part of lead terminals. Thus, there is aparticularly disadvantageous drawback for the case where there is asevere requirement for the miniaturization of electronic circuit.

It is an object of the present invention to eliminate the disadvantagesinvolved in the conventional metallic core wiring substrates asmentioned above, particularly the disadvantages of a decrease in apackaging density for the components and an increase in a height of thelamination. Another object of the present invention is to provide ametallic core wiring substrate which makes a connection between anelectronic circuit provided on the substrate and lead terminals easy andsolves a problem in a case involving further connection thereof withanother printed circuit.

SUMMARY OF THE INVENTION

In order to attain the above-mentioned objects, the metallic core wiringsubstrate according to the present invention has a construction asdescribed hereinbelow. A flat electrically conductive sheet is formed bya method such as etching or the like, into a required shapeincorporating lead terminals and a metallic core such that they arecoplanar, the surface of the electrically conductive substrate iscovered with an insulating material, and thereafter either electricallyconductive patterns are formed on the covering or a printed board havinga completed printed circuit is provided on either or both sides of themetallic core by bonding to the entire surface of the covering by meansof an adhesive, and the wiring patterns are connected with lead terminalbase portions formed on the periphery of the core by the use of, forexample, solder via through holes or the like on the printed board.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a) and (b) are, respectively, a perspective view and a sectionalview taken along the line A--A of FIG. 1(a), showing an example of themetallic core wiring substrate according to the present invention.

FIGS. 2(a)-(f) including FIG. 2(d') are view illustrating amanufacturing process of the example in FIGS. 1(a) and (b);

FIGS. 3(a)-(i) are view illustrating a process for manufacturing ahybrid IC by utilizing the metallic core wiring substrate according tothe present invention;

FIGS. 4(a) and (b) are, respectively, a partial planar view and asectional view taken along the line X--X of FIG. 4(a) illustratinganother example of the present invention;

FIGS. 5(a1)-(a9) are sectional views taken along the line Y--Y of FIG.4(a) illustrating a manufacturing process of the example in FIGS. 4(a)and (b);

FIG. 6 is a sectional view showing a further example for which themetallic core wiring substrate according to the present invention isadapted;

FIG. 7 is a planar view showing a still further example for which themetallic core wiring substrate according to the present invention isadapted; and

FIGS. 8 and 9 are sectional views each showing a further example forwhich the metallic core wiring substrate according to the presentinvention is adapted.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described in detail hereinbelow byreferring to the accompanying drawings.

FIGS. 1(a) and (b) are a perspective view and a sectional view takenalong the line A--A of FIG. 1(a) showing an example of the metallic corewiring substrate according to the present invention wherein baseportions of lead terminals 2 and 3 are provided in the same plane andextend from the side edges of an electrically conductive sheet 1 whichtogether form a core of the substrate wherein the base portions of thelead terminals 2, 3 are in an electrically insulated condition withrespect to the conductive sheet 1 in a manner discussed hereafter, andthese base portions are integrally secured by means of an insulatingcovering 4. Thereafter, electrically conductive patterns 5 are formed onthe surface of said covering 4 by printing or like manner, such requiredpatterns are connected with the surfaces of the lead terminals 2 and 3and further, soldering paste 6 for binding electronic parts is disposedon required positions of the patterns 5.

The metallic core wiring substrate as mentioned above can be easilymanufactured in accordance with the process, for example, as shown inFIGS. 2(a)-(f). More specifically, the conductive sheet 1 having arequired thickness and made of iron, copper, phosphor bronze or the likeis prepared as shown in FIG. 2(a), either a photo resist 7 is applied toor a dry film is bonded to the surface of the conductive sheet 1 (FIG.2(b)), the resulting conductive sheet surface is exposed by the use of arequired mask, the sensitized portions of the photo resist 7 are thenremoved (FIG. 2(c)), and thereafter the sheet 1 thus obtained is etchedto form the base portions of the lead terminal (FIG. 2(d)). In thiscase, the lead terminals 2 (The base portions of the lead terminals 2are preferably formed by cut-outs in the edge portions of the metalliccore which together are arranged in a zigzag manner the cut-outs havinga shape which is more narrow in a direction toward the outer peripherythe substrate and the base portions are wider in a direction extendinginwardly from the outer periphery of the substrate.) have been held witha suitable lead frame 8 which is an extended portion of the substrate 1in such a manner that the lead terminals 2 are not separated from thesubstrate 1 (FIG. 2(d')), and after completing the following coveringprocess with the insulating material 4 (FIG. 2(e)), the lead frame 8 maybe cut off at the positions B and C indicated by each dot-and-dash line.

The insulating material 4 may be provided in such a manner that anadherent high-molecular dielectric material or porcelain enamel issuitably selected, and either the so selected material is applied orprinted by means as a screen printing process.

Then, the required pattern 5 may be printed on the surface of theinsulating covering 4 by using an electrically conductive printing ink,and further, the soldering paste 6 may be printed at the requiredposition on each pattern 5 (FIG. 2(f)).

While the essential construction of the present invention has beendescribed above, electronic parts may also be packaged on the oppositesurfaces of the metallic core wiring substrate according to the presentinvention in order to increase an area for packaging such electronicparts in accordance with the following manner.

FIGS. 3(a)-(i) are diagrams illustrating a manufacturing process for anexample of the substrate wherein through holes are generally required inthe case of packaging electronic parts on the opposite surfaces of asubstrate. In this respect, a photo resist 7 is applied to the oppositesurfaces of an electrically conductive core 1 (FIGS. 3(a) and (b)), eachphoto resist is sensitized through a mask having required patterns (FIG.3(c)), and the so sensitized substrate is then etched to define throughholes 11 (FIG. 3(d)). Furthermore, the wiring substrate of the presentexample may be constructed in such a manner that the opposite surfacesof the resulting substrate 1 with through holes are covered with aninsulating material 4 (FIG. 3(e)), thereafter required electricallyconductive patterns are formed on the opposite surfaces of theinsulating covering 4 by printing with an electrically conductive paste5, and at the same time the paste to maintain a conductive state of theopposite surfaces of the substrate (FIG. 3(f)).

A required electronic part 9, IC or the like is connected with theconductive pattern 5 on the metallic core wiring substrate manufacturedas described above at the required positions (FIG. 3(g)), both the sideedges of the substrate 1 are bent into a dual in-line package (DIP)configuration (FIG. 3(h)), and the electronic part 9 or the like ismolded together with the conductive pattern 5 by utilizing a moldingmaterial 10 such as a plastic material or the like (FIG. 3(i)) to obtaina DIP type hybrid IC.

As a matter of course, the order of the manufacturing process may bechanged, and more specifically, the bending process shown in FIG. 3(h)may be replaced by the molding process in FIG. 3(i), and the bendingprocess in FIG. 3(h) may also be exchanged for the packaging process forthe electronic part 9 or the like in FIG. 3(g).

Moreover, when the lead terminals are provided on either edge of themetallic core wiring substrate, it will be self-evident that a singlein-line package (SIP) type hybrid IC is obtained, although theillustration of the manufacturing processes has been omitted.

In the meantime, a manner for directly applying electrically conductivepatterns to a metallic core wiring substrate is required for such aprocess wherein both the conductive patterns on the opposite surfaces ofthe substrate are connected by means of through holes, or wherein boththe conductive patterns are connected by means of a connecting materialwhich extends a long way around an edge of the substrate in the casewhere packaging for electronic parts is intended to be at a highdensity. In either case, however, its process becomes complicated sothat the above manner is disadvantageous from the point of view of cost.

In order to solve the above problem, a flexible printed circuit in whichwiring has been previously completed may be bonded to the surface of ametallic core wiring substrate wherein lead terminals are provided on atleast one edge of a metallic sheet to be the core by the use of anadhesive.

FIG. 4(b) is a sectional view taken along the line A--A of FIG. 4(a),which is a planar view showing the metallic core according to thepresent invention, illustrating an example for realizing the idea asmentioned above. Lead terminal 2 are provided on the outer periphery ofa metallic sheet 1 to be the core of a substrate at suitable positionsin accordance with the previously mentioned manner such as by etching orthe like and spacings defined between base portions of the leadterminals and the metallic sheet 1 to be the core are insulated andfixed by means of an adhesive. A flexible substrate 13 on which wiringof a printed pattern 12 has previously been completed is bonded to thewhole surface of the core 1 by using the above-mentioned adhesive 4. Inthis case, a through hole 11 is optionally defined on the flexibleprinted substrate 12, 13 at the position corresponding to the baseportion of a lead terminal 2, the adhesive 4 is arranged so as to not bedeposited at this position and the base portion of the lead terminal 2is connected with the wiring pattern 12 by means of solder 14 extendingthrough the hole 11.

In these circumstances, a part 9 to be packaged may be connected andsecured to the printed pattern 12 in accordance with a manner such asreflow or the like.

The metallic core wiring substrate having the construction as describedabove can be easily manufactured in accordance with, for example, such atechnique as described hereinbelow.

FIGS. 5(a1)-(a9) are explanatory sectional views each taken along theline Y--Y of FIG. 4(a) wherein first, a sheet to be core having athickness of 0.1 to 1.0 mm and made of iron, silicon steel, copper,phosphor bronze or the like is prepared, either a photosensitive resin 7is applied to the surface of the sheet or a photosensitive film 7 isbonded to the sheet's surface, after which the sheet is exposed toultraviolet light by the sue of a mask having the required patternswhich are developed to expose only desired portions on the surface ofthe metallic sheet, thereafter the so developed sheet is etched by anormal method. Thus, lead terminals 2 having a desired configuration areformed on the peripheral edge of the core 1. In this case, all the leadterminals 2 are tentatively held by a lead frame 15 in order to preventdisconnection of the lead terminals 2 in the case where the followingprocess is used for removing a remaining photosensitized layer.

Then, an adhesive 4 is printed and applied to the whole surface of thecore except for required portions on the surfaces of the base portion ofthe lead terminals 2 after completing washing and removal of thephotosensitized layer, whereby the base portions of the lead terminals 2are insulated from and secured to the core 1, and further, a flexibleprinted board 13 on which printed wiring as well as formation of throughholes 11 have been previously made as shown in (FIG. 5(a7)) is bonded tothe surface of the core thus processed.

Furthermore, the printed wiring 12 is electrically connected with thelead terminal 2 by means of solder or an electrically conductiveadhesive 14 via the through hole 11.

Required parts are packaged with respect to the metallic core wiringsubstrate manufactured in accordance with the above-mentioned procedureby the reflow technique as described above. In this case, the lead frame15 may, of course, be cut off and removed before or after packaging theparts.

The metallic core wiring substrate according to the present inventionmay be modified as described hereinbelow.

More specifically, flexible printed boards 13 and 13' may be connectedto the opposite sides of a core 1 as shown in FIG. 6. Further, ametallic core double-sided substrate as shown in FIG. 7 may bemanufactured in such a manner that two coplanar sections of a core areprepared so as to obtain a pair of cores 1, 1' and lead frame portions17 are formed at a central folding portion 16. For instance, a suitableperforated or grooved line can be formed on the central portion so as toprovide convenient folding of the pair of cores. Flexible printed boardsare bonded to the surfaces of the left and right cores 1 and 1' on thesame side thereof, respectively, and then the left and right cores arefolded along the folding portion 16 to superpose the two sections andmake the conductive substrate double sided. In this case, the leadframes 17 may be separated from each other to make said cores 1 and 1'electrically independent of one another at the time when lead frames 15,15', which integrally hold the lead terminals 2 as well as 2', are cutoff from the cores 1 and 1'.

Alternatively, a flexible printed board 13 having an insulated printedwiring 12 thereon is bonded to a metallic core wiring substrate so as tosurround a peripheral edge portion thereof as shown in FIG. 8, wherebyit is possible to package required components on the opposite surface ofthe substrate with a high density.

While the above examples have been described with respect to only thecase where a conventional flexible wiring substrate is bonded to ametallic sheet to form a core, the present invention should not belimited thereto. The present invention is also suitable for combiningthe printed board with the core 1 in such a manner that the circuit 12are concentrated on the joined surfaces of the wiring substrate and thecore 1 as shown in FIG. 9, and components are packaged on the surface ofthe substrate at a high density via through holes 11. As a result, it ispossible to easily realize packaging for required components at a highdensity as well as utilization of the core as a large area setting boardby means of the metallic core wiring substrate according to the presentinvention. In this case, when electrical connection between at least onelead terminal and the conductive substrate is maintained, it is alsopossible to ground the conductive substrate through the lead terminal.

INDUSTRIALLY APPLICABLE FIELD

Since the present invention is constructed as described above, it ispossible to inexpensively provide such a printed board which can satisfysevere requirements with respect to packaging of electronic circuits ata high density.

Furthermore, in the present metallic core wiring substrate, the core andthe lead terminals are at the same plane, and in addition, the leadterminals are provided inside the printed circuit part. Accordingly, inthe case where a higher density in packaging of required components isintended for a given space such as when a number of such wiring boardsare vertically mounted on a mother board, and they are connectedelectrically one another, it becomes possible to decrease a height ofthe wiring board by a width corresponding to that of the base portion ofthe lead terminal, which is advantageous from the viewpoint ofdecreasing the entire volume of the electronic circuits.

In addition, the metallic core wiring substrate according to the presentinvention is remarkably effective for constructing a hybrid IC and thelike which require favorable heat release and electrostatic or magneticshielding properties.

While the present invention has been described with reference to theforegoing embodiments, it will be understood that various changes andmodifications may be made thereto which fall within the scope of theappended claims.

We claim:
 1. A metallic core wiring substrate, comprising anelectrically conductive substrate covered with an insulating material, aplurality of leads being coplanar with said substrate and insulatedelectrically therefrom by said covering of insulating material, saidleads being aligned and secured to one longitudinally extending edge ofan outer periphery of said conductive substrate by said covering ofinsulating material, wiring patterns being applied to a surface of saidcovering of insulating material, and means for electrically connectingsaid wiring patterns with said leads.
 2. A metallic core wiringsubstrate as claimed in claim 1, wherein opposite surfaces of saidelectrically conductive substrate are covered with said covering ofinsulating material so as to be capable of packaging electronic parts onthe opposite surfaces of said substrate and said means for electricallyconnecting said wiring patterns to said leads comprises through holes insaid covering of insulating material and in said wiring patterns, saidwiring patterns being provided on said covering of insulating materialon both opposite surfaces of said substrate.
 3. A metallic core wiringsubstrate, comprising an electrically conductive substrate covered withan insulating material, a plurality of leads being coplanar with saidsubstrate and insulated electrically therefrom by said covering ofinsulating material, said leads being aligned and secured to onelongitudinally extending edge of an outer periphery of said conductivesubstrate by said covering of insulating material, a printed boardcontaining printed wiring bonded with adhesive over at least one of twoopposed surfaces of said conductive substrate outside of an area of saidopposed surfaces wherein base portions of said leads are contained, andmeans for electrically connecting said wiring patterns on said printedboard with said leads positioned around said outer periphery of saidsubstance.
 4. A metallic core wiring substrate as claimed in claim 3,wherein said means for electrically connecting said wiring patterns onsaid bonded printed board with said leads around said outer periphery ofsaid substrate comprises through holes in said printed board.
 5. Ametallic core wiring substrate as claimed in claim 3, wherein saidbonded printed board is a flexible printed wiring board, and saidflexible printed wiring board extends around a portion of said outerperiphery of said substrate and covers at least part of each of said twoopposed surfaces of said substrate.
 6. A metallic core wiring substrateas claimed in claim 1, wherein said substrate includes a folding portionthereon which is suitable for bending said substrate into two sectionsand printed boards are bonded to said two sections of said conductivesubstrate with said folding portion therebetween, said conductivesubstrate being bent along said folding portion such that said twosections are superposed to make said conductive substrate double-sided.7. A metallic core wiring substrate comprising an electricallyconductive substrate covered with an insulating material, a plurality ofleads being coplanar with said substrate and insulated electricallytherefrom by said covering of insulating material, said leads beingaligned and secured to one longitudinally extending edge of an outerperiphery of said conductive substrate by said covering of insulatingmaterial, wiring patterns being applied to a surface of said covering ofinsulating material, and means for electrically connecting said wiringpatterns with said leads, said leads aligned on the outer periphery ofthe conductive substrate and the conductive substrate comprising piecesof a single sheet of material which has been separated into said leadsand said substrate.
 8. A metallic core wiring substrate as claimed inclaim 1, further comprising a ground lead coplanar with said substrateand electrically connected thereto, said ground lead being aligned andsecured to said outer periphery of said substrate by said covering ofinsulating material.
 9. A metallic core wiring substrate comprising anelectrically conductive substrate covered with an insulating material, aplurality of leads being coplanar with said substrate and insulatedelectrically therefrom by said covering of insulating material, saidleads being aligned and secured to an outer periphery of said conductivesubstrate by said covering of insulating material, wiring patterns beingapplied to a surface of said covering of insulating material, and meansfor electrically connecting said wiring patterns with said leads, saidcovering of insulating material covering only part of said leads, saidsubstrate including cut-outs, each of which becomes more narrow in adirection towards said outer periphery of said substrate and each ofsaid leads having a base portion located in a respective one of saidcut-outs, said base portion having a width which increases in adirection extending inwardly from said outer periphery of saidsubstrate.
 10. A metallic core wiring substrate as claimed in claim 1,wherein said leads are identical in shape.
 11. A metallic core wiringsubstrate comprising an electrically conductive substrate covered withan insulating material, a plurality of leads being coplanar with saidsubstrate and insulated electrically therefrom by said covering ofinsulating material, said leads being aligned and secured to an outerperiphery of said conductive substrate by said covering of insulatingmaterial, wiring patterns being applied to a surface of said covering ofinsulating material, and means for electrically connecting said wiringpatterns with said leads, said substrate including cut-outs in saidouter periphery thereof and base portions of said leads extending intosaid cut-outs and being insulated from said substrate by said coveringof insulating material.
 12. A metallic core wiring substrate as claimedin claim 3, wherein said substrate includes a folding portion thereonwhich is suitable for bending said substrate into two sections andprinted boards are bonded to said two sections of said conductivesubstrate with said folding portion therebetween, said conductivesubstrate being bent along said folding portion such that said twosections are superposed to make said conductive substrate double-sided.13. A metallic core wiring substrate as claimed in claim 4, wherein saidsubstrate includes a folding portion thereon which is suitable forbending said substrate into two sections and printed boards are bondedto said two sections of said conductive substrate with said foldingportion therebetween, said conductive substrate being bent along saidfolding portion such that said two sections are superposed to make saidconductive substrate double-sided.
 14. A metallic core wiring substrateas claimed in claim 3, wherein said leads aligned on the outer peripheryof the conductive substrate and the conductive substrate comprise piecesof a single sheet of material which has been separated into said leadsand said substrate.
 15. A metallic core wiring substrate as claimed inclaim 3, further comprising a ground lead coplanar with said substrateand electrically connected thereto, said ground lead being aligned andsecured to said outer periphery of said substrate by said covering ofinsulating material.
 16. A metallic core wiring substrate as claimed inclaim 3, wherein said covering of insulating material covers only partof said leads, said substrate includes cut-outs, each of which becomesmore narrow in a direction towards said outer periphery of saidsubstrate and each of said leads has a base portion located in arespective one of said cut-outs, said base portion having a width whichincreases in a direction extending inwardly from said outer periphery ofsaid substrate.
 17. A metallic core wiring substrate as claimed in claim3, wherein said leads are identical in shape.
 18. A metallic core wiringsubstrate as claimed in claim 3, wherein said substrate includescut-outs in said outer periphery thereof and base portions of said leadsextend into said cut-outs and are insulated from said substrate by saidcovering of insulating material.
 19. A metallic core wiring substrate asclaimed in claim 1, wherein at least two of said leads are secured tosaid one longitudinally extending edge of the outer periphery of saidsubstrate and at least two more of said leads are secured to anotherlongitudinally extending edge of the outer periphery of said substrate.20. A metallic core wiring substrate as claimed in claim 3, wherein atleast two of said leads are secured to said one longitudinally extendingedge of the outer periphery of said substrate and at least two more ofsaid leads are secured to another longitudinally extending edge of theouter periphery of said substrate.